Transport213-page5

Transport213-page5 - p can be positive or negative,...

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Transport in Plants - 5 But for a plant it’s not this simple. Plants have that physical pressure against the cell wall (called the pressure potential) that affects water potential. So to determine the movement of water into and out of a plant cell, one needs to have that information, too. True water potential equals the sum of the solute (osmotic) potential plus the physical pressure of the wall, or ± = ± s + ± p What might seem really tricky here for plants is that one can also have a negative pressure or tension (a suction pressure such as we use when we suck beverages through a straw). This means that although ± s is always negative, ±
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Unformatted text preview: p can be positive or negative, although in plants it is always positive, and that affects whether the water potential will be positive or negative. Solute and wall pressure effects on water movement Adding solutes reduces Adding pressure increases water potential Negative pressure water potential decreases water potential Having said a lot, all that we really need to remember here is that water moves from a greater to a lesser water potential and thats important for plants. And when we measure water potential in plants, as we move from soil, to roots to stem to leaves we get a more negative water potential....
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